> Hi, this is a simple question, but why wasn't map or reduce tasks> programmed to be multi-threaded ? ie. instead of spawning 6 map tasks for 6> cores, run one map task with 6 parallel threads.>> In fact I tried this myself, but turns that threading is not helping as it> would be in regular java programs for some reason .. any feedback on this> topic?>> Thanks,> Mark>

Thanks for the reply Nitin, but I don't see what's the bottleneck of havingit distributed with multi-threaded maps ?

I see your point in that each map is processing different splits, but myquestion is if each map task had 2 threads multiplexing or running inparallel if there is enough cores to process the same split, wouldn't thatbe faster with enough cores?

Well... It all depends on where is your bottleneck. Do a benchmark for youruse case if it is critical. Multi-threading might be useful not always. Andyou would rather want to avoid having a locally shared mutable statebecause it can become a pain to manage. But it doesn't mean you can't domulti-threading...